The present invention relates to a sealing sheet assembly and to methods of making and using same. More particularly, the present invention relates to a sheet assembly useful in water and/or gas proofing a surface of a construction which may find uses in various construction and civil engineering applications including, but not limited to, water-proofing constructional surfaces, e.g., roofs, cabins, walls and underground foundation waterproofing, fluid-proofing fluid reservoirs, waterproofing underwater containers, e.g., submarines, and fluid-proofing containers under internal or external pressure, e.g., aircrafts and spacecrafts.
Most particularly, the present invention relates to a multi-layer flexible polymeric sealing sheet bondable to a construction surface, which is less damageable by strains and movements inflicted upon it by the construction surface as compared with the prior art, such that desired sealing capabilities are maintained even under conditions such as massive cracks formation, fissures and/or structural spaces formation within the surface.
The term xe2x80x9cconstruction surfacexe2x80x9d as used herein refers to any surface which is expected to be water or fluid impermeable.
Flexible sheet-like membranes and laminates (referred to herein as xe2x80x9csheetsxe2x80x9d) are frequently used for waterproofing by applying one or more layers of same onto a protected surface. Such sheets are made of a variety of materials, such as, but not limited to, coal tar, bitumen and synthetic polymers, which are formed as sheet-like substances of desired sealing properties. Material and substance properties should meet the requirements of any particular structure, building, authority, climate, chemical and physical environment, required durability, cost effectiveness and the like.
The trend towards irregular roof surfaces, such as, but not limited to, folded plates, hyperbolic paraboloids, domes and barrel shells, has increased the use of plastics or synthetic rubber thermoplastic polymer elastomers as roof coatings. Their advantages include light weight, shape adaptability, good heat reflectivity and high elasticity at moderate temperatures.
Prior art sheets are typically made of thick, flexible and strong materials to prevent their rupture during use. They are either bonded or laid non-bonded over the protected surface.
Bonding is advantageous because lateral massive spread (flood) of water in case of a tear in the sheet is prevented, however, bonding is disadvantageous because, as further detailed below, rapture of the bonded sheet due to cracks formation in the protected surface is readily occurring.
As a result, in many cases a preferred solution for roofing is to lay a loose water-proof sheet, which is not bonded to the surface. This solution is designed to free the membrane from all sorts of stresses caused by sheer and tensile forces resulting from the substrate as a result of thermal and constructive stresses. These forces express themselves often by demonstrating cracks, spaces and fissures which are in widening and shrinking motion (usually cyclic) through the cross-section of the roof or through the walls of the construction.
This motion exhibits a change in the cracks width that tends to increase as a function of many physical factors: e.g., thermal changes or age of the building/construction. In new constructions or after a short period of physical and chemical activities to which the construction is exposed, cracks might appear as a result of climate changes; day and night cycles; extreme changes in temperature; erosion and corrosion of constructive materials; changes in humidity; mistakes in engineering; earth movements; different values of thermal modules of expansion; shrinkage and inflating as a result of vapour pressure, etc.
Often these movements of the construction substrate do not appear in cycles, but expressed as continuous widening of the cracks and spaces or of the expansion joint that are designed to reduce such stresses.
The disadvantages of this concept are that the sheet is subject to elevation and flapping caused by storm wind. Unsolved disadvantage is flooding extensive areas of the protected surface under the sheet, even in the event of a single tiny tear in the sheet. Thus, loose laying is advantageous because the sheet is mostly not affected by cracks formation, however, it is disadvantageous since if a tear should occur massive lateral spread of water is experienced.
Examples of prior art sheets include (i) ethylene propylene diene monomer (EPDM) sheets, which accept about 250%-450% elongation and are typically used at thicknesses ranging between 0.8-1.5 millimeters, mostly in a non-bonded free floating sheet, protected from wind effects by a layer of gravel or concrete placed thereon; (ii) reinforced bitumen sheets, 4-5 millimeters thick, bonded to the surface, which accept 30%-120% elongation and have tensile strength of about 30-80 Kg/5 centimeters; and (iii) plasticized, textile reinforced poly vinyl chloride (PVC) sheets, which accept about 15-25% elongation, 1-2 millimeters thick, having a tensile strength of about 100-160 Kg/5 centimeters, applied mostly as non-bonded free floating sheets, protected from wind elevation by screws or alternatively as bonded sheets being fully bonded to the construction surface.
To illustrate the cracks formation effect upon a protective sheet, consider a crack in a covered surface which grows from 0.05 millimeters in width at the time of application to 3 millimeters thereafter. This represents a 6,000% increase in width. A prior-art, flexible roofing sheet, firmly bonded to the working surface will usually tear under such conditions, causing failure of its sealing properties.
Therefore, wherever massive cracking or strong movement is expected, thicker and/or free-floating (non-bonded) sheets are preferably employed.
In large constructions, thermal and constructive stresses cause tremendous movements, e.g., between constructive roofing elements. In extreme, but quite frequent cases, massive and quick forming cracks, which demonstrate expansion in ranges of thousands percents per hour, cycling on a daily basis, combine shearing action with abrasion upon the sealing sheet. No bonded prior art sheet can withstand these forces without tearing.
When a lower zone of the sheet cross section reaches its maximal elongation ability, rupturing tends to climb along the cross-section, even as a result of smaller changes in stress. Often, a rupture tends to enlarge itself through the whole thickness of the sheet, even without any additional tensile or shear stresses, causing a failure of the sheet.
The use of a strong sealing material will commonly be of no help due to the forceful structural tension.
The cost of a thick monolayer (2.5-4 mm thick) with high and lasting elongation ability (e.g., above 300% after 10-15 years of aging) characterized by chemical and mechanical resistance properties is rather excessive. Such a sheet may provide very good values of bridging ability above small and medium cracks. But, even a 4 mm thick elastic sheet, bonded to the substrate, will not withstand massive movements associated with crack or space formation and/or joints-expansion. When the lower zone of the membrane cross section comes to its maximal elongation ability it ruptures. The rupture tends to progress along the cross-section to the upper surface of the sheet. Most often, the rupture tends to enlarge itself through the whole width of the sheet, even without any additional tensile or shear stresses applied thereto, causing a failure of the coating in the most critic location in the construction, where there is a crack.
Lateral tear resistance of polymeric sheets is not in direct proportion to their thickness. Once an initiation of a long and deep tear is experienced, soon thereafter a total local breaking of the sheet occurs.
Elastic polymers characterized in high elongationability cannot be efficiently reinforced. In such conditions, elastomers and thermoplastic polymers forming a sheet show high values of creeping and fatigue, expressed by decreasing in breaking strengths and other mechanical characteristics that typically cause fast progression of a rupture therethrough. Thermosetic polymers express similar characteristic of failure and fatigue, although their creeping values are usually negligible.
Although the thickness of an elastic thick monolayer sheet provides a large distance between the shear activities generated by the working substrate and the upper surface of the sealing sheet, this costly distance lacks enough shear resistance so as to provide efficient protection to the outer surface of the sheet.
The use of a very elastic, too thin, sheets shows poor bridging ability above massive cracks as a result of the missing thickness and the low abrasion and impact resistance.
The use of infirm bonding of the sheet to the protected surface in many cases demonstrates high frequency of sheet separation as a result of vapour pressure characterizing porosive constructions. Large areas of separation between the sheet and the substrate caused by accumulating shear forces gathered from very large bonded areas along with the disability to control the adhesion strengths to stay inside the narrow margin under temperature changes and aging, cause breaking or too large released areas of the sheet.
Many commercial roof and wall sealing sheets are known.
Chemseal Co., Tel-Aviv, Israel, distributes a two-part sealing compound under the trade name xe2x80x9cELASTOSEALxe2x80x9d. This material is based on polysulphides and on a synthetic rubber Thiokol, which are mixed together and harden into a protective sheet within about two hours after laying. This sealant is however intended to resist various chemicals, as well as water, and is therefore priced higher as compared with other roofing sheets.
Chemiprod, Kibbutz Tel Yitzchak, Israel, distributes a liquid synthetic rubber for roof and wall sealing under the trade name xe2x80x9cLIGOxe2x80x9d, made with a long durability of high elongation to provide waterproofing upon cracked substrate.
South African Surface Coatings, Cape Town, South Africa, distributes a plastic sealant under the trade name xe2x80x9cPOLAROOFxe2x80x9d. This is a trowel-applied material having a 1.28 density when wet and requires two coats and a curing time of 3-7 days.
Both xe2x80x9cLIGOxe2x80x9d and xe2x80x9cPOLAROOFxe2x80x9d are used in thicknesses usually under one millimeters and provide limited ability to overcome major cracks even when thickness is doubled.
Combined layers of different plastics are used to prevent evaporation from water reservoirs. The tearing forces on such floating covers are distributed. These sheets are not configured to be bonded to any surface.
In the past, sealing units incorporating foamed polyurethane or foamed polystyrene have been used because of their thermal properties. However, these materials have an elongation of only about 5% and therefore cannot resist significant compressive deformation This lack of spring-back properties renders these materials inferior for roofing purposes since they are damaged if someone treads thereon. For example, IL Pat. No. 19514 to Allied Chemical Corporation teaches a roof insulation comprising a board-like core of rigid urethane foam, wherein waterproof layers cover each face of the core. This insulation is proposed in thicknesses ranging from 0.6 centimeters to 10 centimeters and has the disadvantage of lacking flexibility to adapt itself to irregular roof shapes or to absorb thermally induced movements in the structure to which it is attached, since urethane is a rigid material of negligible elasticity.
There is thus a widely recognized need for, and it would be highly advantageous to have, a sealing sheet devoid of the above limitations.
According to the present invention there is provided a sealing sheet assembly which can be used to provide a fluid-proof cover for construction surfaces.
According to further features in preferred embodiments of the invention described below, provided is a sealing sheet assembly bondable to a construction surface comprising (a) an upper layer of a first substance, the upper layer being selected fluid impermeable; and (b) a lower flexible layer of a second substance, the lower flexible layer being bondable to the construction surface, the upper layer and the lower flexible layer being at least partially attached to one another; wherein a combination of the upper layer, the lower layer and the at least partial attachment of the layers to one another are selected such that tensile forces resulting from constructional movements acting upon the sealing sheet, result in a local detachment or relative displacement of the upper layer and the lower flexible layer, thereby an ability of the lower flexible layer of transmitting the forces onto the upper layer is remarkably reduced, resulting in improved service of the sealing cover as a whole, the attachment is selected such that a spread of a leakage between the layers via a tear formed in the upper layer is locally restricted.
According to still further features in the described preferred embodiments the combination of the upper layer, the lower layer and the attachments or partial attachment of the layers to one another are selected such that peeling forces acting to separate the layers of the sealing sheet, result in a detachment of the upper layer and the lower flexible layer, such that the upper layer remains substantially undamaged.
According to still further features in the described preferred embodiments the lower layer is capable of at least 200% elongation, preferably it is elastic, however it can also be plastic.
According to still further features in the described preferred embodiments the attachment is capable of at least 200% elongation, preferably it is elastic, however it can also be plastic.
According to still further features in the described preferred embodiments the attachment or the partial attachment includes a formation of closed cells between the layers.
According to still further features in the described preferred embodiments the closed cells having an average area of 1 square millimeter to 100 square centimeters per cell.
According to still further features in the described preferred embodiments the upper layer has a given breaking strength, and the lower flexible layer has a breaking strength at least 60% lower than the given breaking strength of the upper layer.
According to still further features in the described preferred embodiments the upper layer has a given breaking strength, and the attachment between the layers has a breaking strength at least 30% lower than the given breaking strength of the upper layer.
According to still further features in the described preferred embodiments the breaking strength of the lower flexible layer is at least 80% lower than the given breaking strength of the upper layer.
According to still further features in the described preferred embodiments the upper layer has a given thickness, and the lower flexible layer has a thickness at least 65% lower than the given thickness of the upper layer. The thickness of the lower layer is optimally selected between 0.05 millimeters and 0.25 millimeters.
According to still further features in the described preferred embodiments zones which serve for attaching the upper layer and the lower flexible layer encompass about 1% to about 25% of a total area of the sealing sheet assembly, whereas the closed cells encompass about 99% to about 75%, respectively, of the total area.
According to still further features in the described preferred embodiments the zones are arranged in crossing or tangential stripes.
According to still further features in the described preferred embodiments the stripes have a width ranging between 0.1 millimeters and 15 millimeters.
According to still further features in the described preferred embodiments the stripes are substantially linear stripes.
According to still further features in the described preferred embodiments the stripes follow a wave pattern, e.g., sinusoidal pattern, broken line pattern or circles.
According to still further features in the described preferred embodiments the upper layer includes a reinforcing structure (e.g., various woven and non-woven cloths, screens, gauze or free fibers made of materials such as, but not limited to, polyester, glass, polyamide, nylon and carbon fibers) embedded therein.
According to still further features in the described preferred embodiments the reinforcing structure protrudes from a lower surface of the upper layer to form ridges thereon which serve for effecting the partial attachment.
According to still further features in the described preferred embodiments attaching the upper layer and the lower flexible layer to one another to form the closed cells therebetween is effected via an adhesive.
According to still further features in the described preferred embodiments the adhesive is a self adhered pressure sensitive adhesive.
According to still further features in the described preferred embodiments is attaching the upper layer and the lower flexible layer to one another to form the closed cells therebetween is effected via welding.
According to still further features in the described preferred embodiments attaching the upper layer and the lower flexible layer to one another to form the closed cells therebetween is effected via a thermoplastic adhesive screen.
According to still further features in the described preferred embodiments the sealing sheet assembly further comprising a cloth material attached underneath the lower flexible layer and forms a part thereof, the cloth material is bondable to the construction surface.
According to still further features in the described preferred embodiments the sealing sheet further comprising a laminate placed between the upper and lower flexible layers for restricting migration of plasticizers from the upper layer to the lower flexible layer.
According to still further features in the described preferred embodiments the laminate is substantially fully attached to the upper layer, whereby the closed cells are formed between the laminate and the lower flexible layer.
According to still further features in the described preferred embodiments the laminate is attached to the lower flexible layer, whereby the closed cells are formed between the laminate and the upper layer.
According to still further features in the described preferred embodiments the second substance is selected such that the lower flexible layer restricts migration of plasticizers from the upper layer to the construction surface.
According to still further features in the described preferred embodiments the lower flexible layer is a foamed substance.
According to still further features in the described preferred embodiments, a lower surface of the upper layer or an upper surface of the lower layer is formed with ridges which serve for effecting the partial attachment and the formation of closed cells.
According to still further features in the described preferred embodiments the upper layer and the lower flexible layer being substantially fully attached to one another via a week attachment.
According to still further features in the described preferred embodiments the upper layer and the lower flexible layer being further attached to one another sporadically via a stronger attachment.
According to still further features in the described preferred embodiments the weak attachment is effected by an approach selected from the group consisting of weak welding and a use of a weak adhesive.
According to still further features in the described preferred embodiments the weak attachment is effected by an approach selected from the group consisting of weak welding and a use of a weak, preferably water repellent, adhesive, the stronger attachment is effected by an approach selected from the group consisting of stronger welding and a use of a stronger adhesive.
According to another aspect of the present invention there is provided a multi-layer unit designated for being bonded onto a surface of a construction and thereby sealing the surface of the construction and comprising (a) an upper sealing flexible layer having at least it""s outer part protected against chemical and physical environmental influence; and (b) a lower layer bonded to the upper layer, the lower layer being elastic, closed cell, foamed polymeric material having a module of elasticity significantly lower than that of the upper layer and having tensile strength significantly lower than that of the upper layer, the material having an elongation at break of at least 25% in a designated temperature range, and a gas volume in a range of 65% to 99% of it""s total volume. Alternatively, the lower layer is a flexible plastic non-polymeric material, such as, but not limited to, bitumen, modified bitumen rubber, etc. Yet alternatively, the lower layer is a flexible elastic non-polymeric material. Wherein, if the upper layer is thermoplastic or thermosetic, and further wherein if the lower layer has a thickness of above about 2 mm, or if the upper layer is of bitumen, then, the upper and lower layers are selected such that if the tensile strength of the upper layer, according to it""s definition in ASTM Standard D-751, method A (which is incorporated by reference as if fully set forth herein), is expressed in units of Newton per 50 mm width, and the tensile strength of the lower layer, according to it""s definition in Din Standard 53571 (which is incorporated by reference as if fully set forth herein), is expressed in units of Newton per 1 mm squared, then, the ratio between the tensile strength of the upper layer and the tensile strength of the lower layer is greater than 200, whereas, if the upper layer is thermoplastic or thermosetic, and further wherein if the lower layer has a thickness of below about 2 mm, then, the lower and upper layers are selected such that a ratio of the tensile strengths of the upper and lower layers, when expressed in the units, respectively, is greater than 1000.
According to another preferred embodiment of the present invention there is provided a multi-layer unit for bonding onto a surface of a construction mainly a roof deck. According this embodiment of the present invention, the lower and upper layers are selected such that (i) if the tensile strengths of the upper layer according to it""s the standard is below 70 kg to 5 cm, than the lower is selected having a density lower than 60 kg per cubic meter, preferablyxe2x80x94less than 30 kg per cubic meter; (ii) if the tensile strength of the upper layer is below 170 kg to 5 cm, then the lower is selected having a density lower than 70 kg per cubic meter, preferably less than 40 kg per cubic meter ; (iii) if the tensile strength of the upper layer is below 250 kg to 5 cm, then the lower is selected having a density lower than 100 kg per cubic meter preferably less than 50 kg per cubic meter; (iv) if the tensile strength of the upper layer is 350-200 kg to 5 cm (mainly for civil engineering uses) than the lower is selected having a density lower than 160 kg per cubic meter preferably less than 50-70 kg per cubic meter; and (v) if the tensile strength of the upper layer is above 350 kg to 5 cm, then the lower is selected having a density lower than 350 kg per cubic meter. Those density values of the lower layer are for providing a better stress dampening mechanism, that will ensure detachment of the upper layer from the substrate wherever high stresses are transmitted as a result of movements of the substrate in the vicinity of cracks, spaces, fissures and expansion joints in the construction. The detachment will occur by rupture that will develop through the cross section of the lower layer.
According to another aspect of the present invention there is provided a multi-layer unit for bonding onto a surface of a construction and thereby sealing the surface of the construction comprising (a) an upper sealing flexible layer having at least it""s outer part protected against chemical and physical influence; and (b) a lower layer bonded to the upper layer, the lower layer being elastic, closed cell, foamed polymeric material; wherein bonding the upper and lower layers is effected by an adhesive or welding, such that non-bonded closed cells are formed between the upper and lower layers.
According to another aspect of the present invention there is provided a method of attaching a sealing unit to a surface of a construction featuring rough nicrostructure, the method is for fluidproofing the construction, the method comprising the steps of (a) providing a sealing unit featuring an elastic, foamed, polymeric lower layer and an upper layer bonded thereto, the lower layer featuring a compression-deflection properties; (b) spreading an adhesive over the surface, the lower layer or both; (c) placing the sealing unit over the surface such that the lower layer faces the surface; and (d) applying pressure over the sealing unit; wherein the compression-deflection properties of the lower layer and the pressure are selected such that the lower layer penetrates into the microstructure of the surface, to thereby form a substantially continuous contact therebetween, so as to improve bonding of the sealing unit to the surface, while reducing adhesive quantities required therefor.
The present invention successfully addresses the shortcomings of the presently known configurations by providing a sealing sheet assembly which is more durable as compared with prior art sheets although it is bounded to the protected surface, such that when it tears, no uncontrolled massive flood is experienced.